Diabetes, notably type 1 and type 2 diabetes, together with obesity, which is believed to be a major causal factor in development of, in particular, type 2 diabetes, constitute a growing and worldwide major health problem. Diseases or disorders that may develop as a consequence of untreated diabetes include cardio-vascular and peripheral artery disease, micro- and macrovascular complications, stroke and possibly certain forms of cancer.
Diabetes is characterized by a defective physiological regulation of blood glucose levels, and among under-lying conditions that may lead to diabetes are reduction in or loss of pancreatic β-cell mass and function, with attendant reduction in or loss of endogenous Insulin production, and/or Insulin resistance (reduced sen-sitivity to Insulin), i.e. reduction in or loss of the ability of endogenous Insulin to bring about adequate regulation of blood glucose levels.
A number of hormones that lower blood glucose levels are secreted by the gastrointestinal mucosa in response to the presence and absorption of nutrients in the gut. These include glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP) and Secretin.
GLP-1 [see, e.g., Ørskov, Diabetologia 35: 701-711 (1992)] is produced by tissue processing of proglucagon, a 180 amino acid peptide [see, e.g., Drucker, Diabetes 47: 159-169 (1998)]. The overall sequence of proglucagon contains the 29 amino acid sequence of glucagon, the 36 or 37 amino acid sequence of GLP-1, as well as the 34 amino acid sequence of glucagon-like peptide-2 (GLP-2; an intestinotrophic peptide). Human GLP-1(7-37) has the amino acid sequence HAEGTFTSDVSSYLEGQAAKEFIAWLVKGRG (SEQ ID NO: 114).
GLP-1 has been identified as having a number of functions. It is a hormone that enhances glucose-stimulated Insulin secretion in normal humans (and therefore belongs to a group of hormones known as incretin hormones). In addition, GLP-1 lowers glucagon concentrations, delays gastric emptying, stimulates (pro)Insulin biosynthesis, and enhances Insulin sensitivity [see, e.g., Nauck, Horm. Metab. Res. 47: 1253-1258 (1997)]. GLP-1 also enhances the ability of pancreatic β-cells to sense and respond (by Insulin secretion) to glucose in subjects with impaired glucose tolerance [see, e.g, Byrne, Eur. J. Clin. Invest. 28: 72-78 (1998)]. The insulinotropic effect of GLP-1 in humans increases the rate of glucose disappearance and decreases endogenous glucose production, partly because of increase in Insulin levels and partly because of enhancement of Insulin sensitivity [see, e.g., D'Alessio, Eur. J. Clin. Invest. 28: 72-78 (1994)]. However, the short half-life of native GLP-1 in vivo has constituted a major pharmacological challenge in attempts to exploit the hormone as a drug. In humans and rats, GLP-1 is rapidly degraded by dipeptidyl peptidase-IV (DPP-IV) to GLP-1(9-36)amide, that acts as an endogenous GLP-1 receptor antagonist. Several strategies for circumventing this problem have been proposed, some of which employ inhibitors of DPP-IV, while others employ DPP-IV resistant analogues of GLP-1(7-36)amide.
The so-called Exendins, which constitute another group of peptides that lower blood glucose levels, have some sequence similarity (53%) to GLP-1(7-36) [see, e.g., Goke et al., J. Biol. Chem. 268: 19650-19655 (1993)]. The Exendins are found in the saliva of Helodermatidae species (beaded lizards). Exendin-3 is present in the saliva of Heloderma horridum (Mexican beaded lizard), while Exendin-4 is present in the saliva of Heloderma suspectum (Gila monster). The amino acid sequence of Exendin-4, which differs from that of Exendin-3 at positions two and three, is HGEGTFTSDLSKQMEEEAVRLFIEWLKNGGPSSGAPPPS-NH2 (SEQ ID NO: 115).
Exendin-4 has been reported to be a potent GLP-1 receptor agonist on isolated rat insulinoma cells [Goke et al., loc. cit.]. WO 99/07404 discloses that Exendin-4 administered systemically lowers blood glucose levels by 40% in diabetic db/db mice, and a long-lasting blood glucose lowering effect of once-daily intraperitoneal injection of Exendin-4 in diabetic ob/ob mice has also been reported [Grieg et al., Diabetologia 42: 45-50 (1999)].
U.S. Pat. No. 5,424,286 and WO 98/05351 disclose that Exendin-3, Exendin-4 and Exendin agonists may be used for the treatment of diabetes, for reducing gastric motility and delaying gastric emptying, and for prevention of hyperglycemia, and WO 98/30231 further discloses that they may be used for reducing food intake.
The peptide hormone Gastrin is secreted from cells in the gastric mucosa and from G cells in the duodenum, and among the major physiological roles of the hormone in humans are stimulation of secretion of gastric acid (i.e. NCI) and aiding in gastric motility. Other identified effects of Gastrin include stimulation of cell growth, and there are indications that Gastrin may play a role in islet neogenesis, i.e. stimulation of Insulin-secreting β-cell growth in the pancreatic islets [see, e.g., Korc, M., J. Clin. Invest., 92: 1113-1114 (1993); Rooman et al. Diabetes 51: 686-690 (2002)], and thereby contribute to regulation of blood glucose.
Gastrin shares receptors with another gastrointestinal peptide hormone, Cholecystokinin (CCK). The receptors CCK-A R and CCK-B R have different affinities for Gastrin and CCK variants. CCK-A R (or CCK R1) acts primarily as a receptor for sulfated CCK, whereas CCK-B R (or CCK R2) binds both CCK and Gastrin equally well. CCK-B R is considered to be the “Gastrin receptor” due to the higher levels of Gastrin compared to CCK in plasma [Foucaud et al. Reg. Peptides 145: 17-23 (2008)].
CCK-B R can initiate several intracellular pathways upon binding of ligand, which is considered to be the reason for the diverse physiological roles of CCK. A key pathway downstream of CCK-B R is the MAPK (mitogen activated protein kinases) or ERK (extra-cellular regulated kinases) pathway, which is also activated by several growth hormones. This is a key feature in the cell proliferation role of Gastrin. Since CCK-B R is expressed in the pancreas, Gastrin is able to contribute to cell proliferation and islet regeneration in this tissue.
In humans, Gastrin occurs primarily in three forms, viz. Gastrin34, Gastrin17 and Gastrin14 (with reference to the total number of amino acids in the sequence in question). Gastrin6 has also been identified. The shorter forms are generated by cleavage of C-terminally amidated Gastrin34; thus Gastrin17 consists of the C-terminally last 17 residues of Gastrin34 (corresponding to Progastrin (55-71), Gastrin14 the C-terminally last 14 residues (corresponding to Progastrin(58-71), and Gastrin6 only the C-terminally last 6 residues (corresponding to Progastrin(66-71). It is the amidated forms of Gastrin that bind with high affinity to CCK-B R and exert cell proliferative functions. In human Gastrin17 the N-terminal amino acid residue is a pyroglutamic acid (PyroGlu) residue. The amidated C-terminal 6 amino acids are the key receptor-binding residues of Gastrin.
WO 2005/072045 discloses, inter alia, combinations of “GLP-1 agonists” and “Gastrin compounds” reputedly having beneficial effects in the prevention and/or treatment of conditions and/or diseases for which either a “GLP-1 agonist” or a “Gastrin compound” have been demonstrated to have a therapeutic effect. WO 2007/095737 discloses, inter alia, analogous combinations of “Exendin agonists” and “Gastrin compounds” that reputedly likewise have beneficial effects in the prevention and/or treatment of conditions and/or diseases for which either “Exendin agonists” or “Gastrin compounds” have been demonstrated to have a therapeutic effect.
Data [deriving from studies employing non-obese diabetic (NOD) mice, widely employed as an animal model for human type 1 diabetes] presented in WO 2005/072045 appear to indicate that certain “GLP-1 agonist”/“Gastrin compound” combinations described therein may have a beneficial effect with respect to normalizing blood glucose levels in acutely diabetic NOD mice compared to the effect seen when employing the “GLP-1 agonist” (or the “Gastrin compound”) in question alone. Data [likewise deriving from studies employing non-obese diabetic (NOD) mice] presented in WO 2007/095737 appear to indicate that certain “Exendin agonist”/“Gastrin compound” combinations described therein may have a beneficial effect with respect to normalizing blood glucose and Insulin levels in acutely diabetic NOD mice compared to the effect seen when employing the “Exendin agonist” (or the “Gastrin compound”) in question alone, and that certain “GLP-1 receptor agonist”/Gastrin combinations described therein may have a beneficial effect with respect to inducing islet cell regeneration compared to the effect seen when employing the “GLP-1 receptor agonist” alone.
WO 2005/072045 and WO 2007/095737 also disclose the possibility of forming conjugates comprising a “GLP-1 agonist” or “Exendin agonist”, respectively, and a “Gastrin compound” covalently coupled or linked (i.e. conjugated) to one another, optionally via an intermediate linker or spacer. As a suitable spacer is mentioned a mono- or disaccharide, an amino acid, a sulfate, a succinate, an acetate, or an oligomeric polymeric spacer or linker comprising one or more of such moieties. Contemplated methods by which conjugates of the types in question might be prepared are also described. However, no preparative or other data are provided in either of the latter documents in question to substantiate that any conjugate of the type in question had in fact been prepared and characterized—or tested with respect to its biological/physiological properties or activity—at the time of filing of the respective international application.
It may further be noted that neither WO 2005/072045 nor WO 2007/095737 provide any in vivo, in vitro or other data to substantiate that the “GLP-1 agonist”/“Gastrin compound” or “Exendin agonist”/“Gastrin compound” combinations, respectively, described and utilized therein might be beneficial in the treatment, for example, of type 2 diabetes.